Lithium Difluoro(oxalato)borate as Additive to Improve the Thermal Stability of Lithiated Graphite

The reaction of lithiated graphite with a nonaqueous electrolyte of 1.2 M LiPF6 in ethylene carbonate/ethyl methyl carbonate (3:7 by weight) was investigated using differential scanning calorimetry. The decomposition of the solid electrolyte interphase (SEI) took place at about 100 degrees C and was followed by a continuous formation/decomposition of the SEI up to 250 degrees C. Another two peaks were observed at temperatures above 250 degrees C. These peaks were attributed to the major reaction of lithiated graphite with the nonaqueous electrolyte. With the addition of lithium difluoro(oxalato)borate as an electrolyte additive, the onset temperatures of the three peaks were pushed higher, as confirmed by the activation energies obtained.